Enhancing quality assurance in external radiation therapy: A study on the use of EPID ASi1200 and ArcCHECK® phantom in VMAT plans

Introduction

Volumetric modulated arc therapy (VMAT) offers precise dose delivery through dynamic modulation. However, its complexity necessitates robust quality assurance (QA) procedures. This study evaluated the Electronic Portal Imaging Device (EPID) ASi1200 and ArcCHECK® phantom in verifying VMAT plans for multiple anatomical sites.

Methods

A total of 73 VMAT treatment plans (brain, abdomen, thorax, pelvis, and head and neck) generated in the Eclipse treatment planning system (TPS) and delivered via the TrueBeam STx linear accelerator were evaluated. The calculated doses were verified using both EPID ASi1200 and ArcCHECK® systems. Gamma index analysis was performed with a 3 %/3 mm criterion and a 10 % threshold. Statistical analyses, including paired t-tests, normality testing, and Spearman correlations, were conducted to compare the agreement between the two systems across anatomical sites.

Results

Both verification tools achieved high Gamma pass rates (>99 %). EPID showed significantly higher agreement in pelvic plans (p < 0.001), while differences in other sites were statistically non-significant or clinically negligible (<0.3 %). Correlations between systems were weak to moderate, indicating complementary rather than interchangeable outputs.

Conclusion

EPID and ArcCHECK® are both reliable for VMAT QA, with EPID offering a distinct advantage for pelvic plans. Either tool may be sufficient for routine verification, but dual-method QA is advisable for highly modulated or clinically critical cases.

Implications for practice

EPID can serve as the primary QA method for pelvic cases, streamlining workflow without compromising accuracy, while site complexity should guide tool selection elsewhere.